πI recommend the following novels to you: "The Strongest Forbidden Zone that Covers the Sky" and "The Greatest Evil Practitioner" are both fantasy novels. The main characters are cold and ruthless, and they kill decisively. They meet your requirements. The protagonist of "The Strongest Forbidden Zone" was a fully formed Saintly Being who was torn apart. He broke through the door of the Imperial Pass and killed decisively. There was no female protagonist in the whole story. The protagonist of "The Most Evil Practitioner" was called Xie. The story began with a long-planned, extremely cruel, and inhuman genius murder case. The cold and cruel protagonist met your requirements. I hope you like this fairy's recommendation. Muah ~π